Hydrofoil craft



March 1, 1960 P. LEEHEY 2,926,623

' HYDROFOIL CRAFT Filed June 12, 1957 2 Sheets-Sheet 1 1 INVENTOR v v N PATRICK LEEHEY I. a I

ATTORNEYS March 1, 1960 P. LEEHEY 2,926,623

HYDROFOIL CRAFT Filed June 12, 1957 v a T 2 $h9tS-Sh69t 2 HEAVE AMPLITUDE MAGNIFICATON VS. WAVE LENGTH (23 2.5 p 7 MQQELA 3 TANDEM VEE-FOILS Fonza. AFT L: 20 5 m1: TANDEM vazmus 2 1.5 mam- PLUS u FLAT MID FOIL Q AT/QG. D l. 5 'm g VEE-FOlL FORWARD, FLAT- FOIL AFT m S I WAVE LENGTH IN PITCH AMPLITUDE MAGNIFICATION VS. WAVE LENGTH mDEL A TANDEM VEE-FOILS FORE & AFT

I mDEL fi TANDEM VEE-FOILS FORE 8'AF T PLUS FLAT MID-FOIL AT C.G

A C VEE-FOIL FLAT FOIL AFT PITCH AMPLITUDE MAGNIFICATION WAVE LENGTH lN FEET INVENTOR PATRICK LEEHEY ATTORNEYS (Granted under Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used. by or for the Government of the United States for governmental purposes withoutthe payment of any royalties thereon or therefore.

This invention relates to hydrofoil boats wherein the hull in intended at high speeds to rise in the water and so reduce resistance to the forward motion of the boat.

6 More particularly, this invention relates to the relative location of a plurality of hydrofoils beneath the hull of a boat.

Orginally, in common designs ofhydrofoil craft, the hydrofoils were located with little or no thought given a to wave motion. The hydrofoils were orginally located in amanner that the effect of rapid motion has been to raise the bow of the boat resulting, however, in increase in the draft of the stern and even though the surface of the hull presented to the water had been decreased, this depression of the stern was undesirable, and if avoided a greater speed of the boat could be attained.

Various designs for elevating the depressed stern have been proposed. These proposed designs have included additional hydrofoils and/or the location of a hydrofoil directly beneath the stern and to the rear of the propeller, and while these advances in the hydrofoil art have had some success in more nearly maintaining the hull of a boat in horizontal position in relatively quiet waters, they have not, insofar as applicant can determine, been very satisfactory in disturbed waters, particularly in following gseas.

In a series of experiments on the motions of hydrofoil craft in waves in a towing tank, conducted at the David Taylor Model Basin by applicant, two conventional configurations of hydrofoils were tested. One model used tandem Vfoils of 45 degrees dihedral equally spaced fore f and aft of the center of gravity of the craft. The other model used a V-foil of 45 degrees dihedral forward and asubmerged fiat foil aft. The results of tests of these configurations and arrangements confirmed applicants previous theoretical and experimental conclusions that conventional area-stabilized hydrofoil configurations performed poorly in following waves because:

(a) They have a lightly damped natural mode of I longitudinal oscillation which is excited by waves of encounter frequency near the frequency of the configuration and the encounter frequency is reduced by following waves for any given speed thus giving the craft more time to respond to the waves by pitching and/ or heaving; and, simultaneously (b) The orbital velocities of following waves cause a detrimental phase lag in the oscillatory lift, that is since the orbital motion of the water particles in the back slope of a wave is downward, lift is reduced as the foil approaches a wave crest and since the orbital motion of water particles under the forward face of the wave is upward, lift is increased as the foil approaches a wave trough.

Thus it is seen that orbital velocities in following waves U tatCS r 2,926,623 Patented Mar. 1,. 1960 cause an upward thrust on the hydrofoil while it has its maximum angle of attack and maximum lift, that is, just after it crosses a wave crest, and causes adownward thrust on the hydrofoil at the momentwhen it has its minimum angle of attack and minimum lift, that is, just after it crosses the bottom of a trough. Thiseffect magnifies the wave action on pitching and heaving motion of the craft.

From the above experiments, tests and deductions, applicant conceived a foil arrangement including a flat midfoil placed substantially at the centerof gravity of the craft with V-foils spaced equidistant fore and aft of the center of gravity. With this arrangement, in following seas of wave length approximately equal to the spacing between. the forward and after foils (3' feet in the experimental models) applicant visualized the orbital wave effect on the lifting of the mid-foil as being almost precisely degrees out of phase to the orbital wave effeet on the lift'of each of the two end foils. The heave response of this configuration to such following waves could therefore be rendered negligible by using a mid-foil with inherently greater rate of change of lift with change in angle of attack than that of the two end foils. If, further this is done for a configuration whose natural frequency of longitudinal oscillation at design speed is near the frequency of encounter at design speed for following waves of length approximately equal to the spacing between the forward and after foils, the peak heave amplitudemagnification which would otherwise result from conditions (a) and (b), referred to above, could be reduced considerably and the overall performance in following waves would be greatly improved. A configuration of this type was tested and its measured heave and pitch responses to waves were compared to those of the aforementioned two conventional configurations as shown in graphs to be referred to hereinafter. The results show that both heave and pitch response are greatly reduced forthe mid-foil configuration for following waves of length'near 3 feet, the length of the model. At other wave lengths in both ahead and following seas, the additional dynamic damping afforded by the mid-foil results in a moderate reduction in heave and pitch amplitude magnification.

It is therefore a broad object of this invention to improve the stability of hydrofoil craft. 1

A further object of this invention is to improve the performance of area-stabilized hydrofoil configurations in following waves.

A more specific object of this invention is to provide a hydrofoil craft with hydrofoils having hydrodynamic characteristics so chosen as to permit flight through following seas of wave length near craft length with little or no heave or pitch amplitude magnification.

Other objects and many of the attendant advantages becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

Fig. 1 is aperspective view of the hull of a boat incorporating a preferred embodiment of the invention;

Fig. 2 is a reproduction of a graph showing the relationship of heave amplitude magnification to wave length for three hydrofoil configurations in ahead waves and in following waves; and i Fig. 3 is a reproduction of a graph similar to that of Fig. 2 and showing the relationship of pitch amplitude magnification to wave length.

In Fig. 1 of the drawings, 10 indicates the hull of a vessel provided with a propeller 12 mounted on a propeller shaft 14 and driven by a suitable power plant, not shown. The propeller shaft passes through a tubu 3 lar casing 16 supported from the bottom of the hull by a vertical strut 18.

In accordance with this invention, three hydrofoils 20, 22.and.24 are mountedzintandem on the. bottom of the hull by. suitable meansnot shown.. As shown; each of the threehydrofoilsextends transversely of the longitudinal axisQOf the'hiilllwiththe.mid-foil'22 located in or substantially'in a-transverse vertical plane through the center of gravity, [CG of the hull, and with the hydrofoils 20 an'd124 spaced equidistant fore and aft, respectively, of the center of gravity. p

.The. fore and ,aftv hydrofoilsare shown as .v-foils of 45. .'degrees dihedral with suitable angle of attack on the-V portio'ns 20'A and 24A and with streamlined vertica'lfstruts 20B and 243, respectively. The fore and aft hydrofoils" are not limited to theV-shape shown and may begiven other shapes. The mid-foil 22, however, should havea rather extensive flat section 22A and a sufficient number of streamlined'verticallstruts ZZB'for stability. Since the mid-foil is used normally. for stability rather than lift, thefi'dtsectionZZA thereof need have little if any,angle of attack. As shown, the center vertical strut of the mid-foil may be-used as an auxiliary support for the tubular casing 16 of the propeller shaft,.and the stern ,endof the shaft'may be supported by the aft'foil 24.

The effects on heave and .pitch amplitude magnification, resulting from the. addition of the mid-foil in accordance with this invention, are graphically illustrated in Figs. 2 and 3.' As stated heretofore, three models were tested. Each 'model was of the same length, three feet. Model A, represented by curves A (Figs. 2 and 3) comprised a conventionalT'configuration with tandem \l-foils of 45 degrees dihedral equally spaced fore and aft of the center of gravity of the model. Model A might be said to be generally similartothe arrangement illustrated in -Fig'; l,'with the mid-foil eliminated. Model B, represented by curves 13 (Figs. land 3), was in accordance with this invention and included tandem 'V-foils of 4S degrees'dihedral equally spaced fore and aft of the center of gravity, with the added fiat, mid-foil at the center of gravity. Model B might 'be said to be substantially the same as .that illustrated in Fig. 1. Model C, represented by curves C (Figs. 2 and 3)"comprised a V-foil of 45 degrees dihedral forward and a submerged flat foil aftequally spaced from the center of gravity of the model. 'Model C might be visualized in Fig. 1 by removing the fiat foil from its midposition and using it to replace the aft V-fo'il. I

In following waves, as shown in Fig. 2,..model B, curve B; shows ,a vast improvement over conventional m'od'elsA and C, 'in' that model B approaches an optimum low heave amplitude magnification in wave lengths of three feet. In ahead .waves the. differences in, heave amplitudei magnification of the three models is .not so pronounced;but; here again model B shows anjmprovcment over'modelsiA and C when subjected to wave lengths of three feet:

Differences in pitch amplitude .magnification ,of the three models" is shown in Fig. 3. Here, in following 'waves, models A and B show relativelylow pitch amplitude magnification, in wave lengths of three feet, as compared with model C, with model B the lowest of the three. In ahead waves of three feet, the pitch amplitude of the three models is not appreciably different. However, model B shows an improvement over models A and C.

Thus, it is shown with applicants invention with a fiat mid-foil located at the center of gravity of the craft, and with V-foils or similar surface-piercing foils located equidistant fore'and aft of the center of gravity, both heave and pitch response are greatly reduced for following waves of length near that of the spacing of the foils. At other Wave lengths in both ahead and. followingqseas, the additional dynamic damping afforded by the mid-foil results in an appreciable reduction in heave and pitch amplitude magnification.

It should be understood, of course, that the foregoing disclosure relates to only a preferred embodiment of the invention and that numerous modifications or alterations maybe made therein without. departing frornthespirit and the scope of the invention as setforth in the appended claims.

What is claimed is:

1. A hydrofoil boatrcomprising a hull having-a determinable center, .of gravity, a propeller and propeller shaftfor driving said propeller,; and a plurality of hydrofoilsattached ,to the hull projecting vertically downward therefrom and extending transversely tothe longitudinal axis of the hull, said plurality of hydrofoils including a fixed mid foilplocated substantially in avertical plane' through the center of gravity of the hull and-perpendicular to the longitudinal axis :of the'hull, said mid-foil having an extensive fiat section; a plurality-0f streamlined. surface-piercing vertical strutssupporting I said mid-foil so that it isv normally submerged, and normally has substantially no angle of attack; .said pluralitvof vhydrofoils further including a pair of fixedsurfaee piercing hydrofoils spaced at equaldistances foreand after": the center of gravity, said surface-piercing foils beingrnounted on said hull in a manner to provide surh'cient angle. of attack to lift-said craft as said craft is propelled forward through a body of water whereby said surface-piercing foils provide lift relative to the Water while said midefoil provides dynamic damping of pitch and, heave amplitude of the craft 2. The invention as defined in claim 1 andfurther including a tubular propellershaft casing supported by one of said plurality of vertical struts supporting-said mid-foil.

References Cited-in the tile of this patent UNITED STATES PATENTSv 1,720,167 Clifton July 9,1929

2,257,405 Burtenbach Sept..30, 1941 2,767,678. Verte'ns h Oct. 23,, 19,56

FOREIGN PATENTS 517,518 Germany Feb. .4, 1931 768,l08 Germany Aug. 4, 1955 

